A. Field of the Invention
This invention relates to the field of art of oscillators stabilized with respect to varying supply voltage values.
B. Prior Art
Many prior schemes have been used to achieve oscillations suitable for digital counting operations such as those used in clocks. However, such former techniques possess particular shortcomings with respect to frequency stability over a wide range of supply voltage values as is commonly experienced in the automobile clock circuit. A wide operating voltage range occurs in automobile environments due to reasons such as (1) severe current drain demends on the battery during cold weather engine starting attempts, (2) poor regulator performance, and (3) generator deficiencies with increasing age.
One of the basic problems inherent in the operation of the prior art devices is the stabilization of the operation point of the active amplification device in the presence of 6 to 1 changes in the supply voltage. Reliable start-up behaviour at extremely low supply voltages, as for example, 3 volts, is another critical shortcoming of prior devices. A further performance shortcoming exists with respect to the purity of the sinusoidal waveform developed by prior art devices since these devices utilize large signal swings in the active devices of the oscillator network. Large signal amplification involves non-linearities and clipping at signal extremes. Another shortcoming of prior art devices is that the current in the oscillator has varied as approximately the square of the supply voltage.